The processes involved in the conversion of chemical energy into heat and mechanical work by contracting muscles will be studied using the energy balance technique. These studies will be accomplished by measuring the time course of muscular energy liberation, using myothermometry, and comparing it to the time course of high energy phosphate utilization as determined from chemical analyses of rapidly frozen muscles. These techniques permit assessment of the extent to which the reactions though to occur in the muscles account for the observed energy liberation. It is currently believed that the only significant source of muscular energy liberation is the hydrolysis of ATP by the myofibrils (crossbridges) and the sarcoplasmic reticulum. However, there is evidence indicating that the redistribution of calcium per se to different binding sites in the muscle during activation may produce significant amounts of energy. Experiments are designed to test and extend this idea and a hypothesis to account for the observed thermal behavior is advanced which will be tested by comparing the kinetics of an enthalpy production by calcium binding to proteins (parvalbumin) isolated from muscles. There is also evidence that changes in the crossbridge distribution during transitions from one type of contraction to another can result in the production and/or absorption of significant amounts of energy which takes place over a relatively long period of time (0.1-1.0 sec). The time course of such crossbridge distribution changes in a variety of types of contraction (varying velocity of shortening, lengthening, etc.) will be examined using the energy balance technique and by myothermometry. The results will be related to published theories of the mechanism of contractile protein ATPase. To more closely relate such changes to the mechanism of high energy phosphate by the crossbridges, contractile protein will be isolated from frog muscles and the mechanism of their ATPase studied using steady state and transient kinetic techniques. Our experiments are expected to provide new information about the ways muscles liberate energy, consume ATP, and how crossbridges cycle and calcium ions circulate within the cell.